The present invention relates to a device and to a method for hardening foundry cores of sand-containing molding materials, wherein the core, for its hardening, is subjected in a core molding tool to a catalyst vapor/carrier gas mixture by means of a gassing plate which can be coupled to the core molding tool in a gas-tight manner and subsequently to a pressurized air stream, each at a predetermined pressure and predetermined temperature.
(1) Field of the Invention
Such cold hardening methods and devices are known, for example, the so-called cold box method, in which two components of a synthetic resin system are added to the core sand, which then harden along with the sand as soon as an organic catalyst, such as an amine, for example, an alkylamine or a methyl formate, is added as catalyst.
Here, one of the components could be, for example, a polyester resin, a polyether resin or any synthetic resin having a fluid consistency with reactive hydroxyl groups; the second component in any case is an organic isocyanate. The two components are thoroughly mixed with the mold sand and then formed. In order to then catalyze the reaction and to design the handling and the use of particularly the amines reliably, various efforts have been undertaken to date.
(2) Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
However, the known methods and devices have a disadvantage in common in that the hardening process is very time consuming. For example, the forming of the core-sand mixture in the molding tool on a core shooting machine often takes only fractions of a second, whereas the subsequent gassing for hardening the core has to take place over several seconds, which naturally makes the gassing an enormous cost factor.
In order to reduce the gassing time or the hardening time, the proportion of the amines as a rule has been dosed in excess, with the risk that a renewed dissolution of the binder could occur, lowering the potential final strength of the core to approximately 80 to 85%.
In an additional method or device (EP 0229959 of the same applicant), dosing pumps are inserted between the catalyst source and the mixing site of the carrier gas and the catalyst, in order to be able to better dose the catalyst; however, this too can only lead to an unsatisfactory result, since the pressure conditions in the catalyst feed in each dosing process at first are completely without effect.
In addition, it has been proposed (CH Patent 603276 of the same applicant) to temporarily store both the catalyst vapor/carrier gas mixture and also the pressurized air each in a dosing container and then to perform the shooting successively in bursts from this dosing container into the core, wherein the pressurized air is stored with a greater volume and heated to a higher temperature than the catalyst vapor/carrier gas mixture.
However, the technical effort is enormous for these measures, and installations of this type allow few variables.
Furthermore, EP 0881 014 of the same applicant describes a method and a device of the above-mentioned type, in which the valve means comprise a multipath valve in the feed line of the storage tank, which can be rerouted temporarily to a return line to the storage tank for the pressure equalization in the feed system.
These measures make it possible to keep the pressure conditions in the catalyst feed constant in each dosing process, after a pressure equalization is carried out in each case beforehand.
Furthermore, EP 1 375 031 B1 of the same applicant describes a method and a device of the above-mentioned type, in which preheated pressurized air is fed through a switching valve to a heating and mixing stage and to a reheater through a line for further heating for the flushing. The advantage of this device or of this method is that the pressurized air for a gassing, with increasing heating of the catalyst vapor/carrier gas mixture, can be heated variably, in order to achieve a so-called contour hardening. One disadvantage of this device is that a precise monitoring of the temperature is required in order to ensure the safety of the installation.
Thus, the problem of the present invention is to provide a method for hardening foundry cores of sand-containing molding materials, and to provide a corresponding device by means of which, at constant speed or cycle time, a strong reduction of the emission at the work site is ensured by reduced catalyst consumption. Furthermore, as a result, the disposal costs and the cleaning effort for the device should be reduced and thus considerably lower environmental pollution should be achieved. In addition, the installation should be cost effective.